1 /*
2 * Copyright (c) 2001 Markus Friedl. All rights reserved.
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions
6 * are met:
7 * 1. Redistributions of source code must retain the above copyright
8 * notice, this list of conditions and the following disclaimer.
9 * 2. Redistributions in binary form must reproduce the above copyright
10 * notice, this list of conditions and the following disclaimer in the
11 * documentation and/or other materials provided with the distribution.
12 *
13 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
14 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
15 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
16 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
17 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
18 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
19 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
20 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
21 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
22 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
23 */
24
25 #include "includes.h"
26 RCSID("$OpenBSD: kexdh.c,v 1.18 2002/03/18 17:50:31 provos Exp $");
27
28 #pragma ident "%Z%%M% %I% %E% SMI"
29
30 #include <openssl/crypto.h>
31 #include <openssl/bn.h>
32
33 #include "xmalloc.h"
34 #include "buffer.h"
35 #include "bufaux.h"
36 #include "key.h"
37 #include "kex.h"
38 #include "log.h"
39 #include "packet.h"
40 #include "dh.h"
41 #include "ssh2.h"
42
43 void
44 kexdh_server(Kex *kex)
45 {
46 BIGNUM *shared_secret = NULL, *dh_client_pub = NULL;
47 DH *dh;
48 Key *server_host_key;
49 u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
50 u_int sbloblen, klen, kout;
51 u_int slen;
52
53 /* generate server DH public key */
54 dh = dh_new_group1();
55 dh_gen_key(dh, kex->we_need * 8);
56
57 debug("expecting SSH2_MSG_KEXDH_INIT");
58 packet_read_expect(SSH2_MSG_KEXDH_INIT);
59
60 if (kex->load_host_key == NULL)
61 fatal("Cannot load hostkey");
62 server_host_key = kex->load_host_key(kex->hostkey_type);
63 if (server_host_key == NULL)
64 fatal("Unsupported hostkey type %d", kex->hostkey_type);
65
66 /* key, cert */
67 if ((dh_client_pub = BN_new()) == NULL)
68 fatal("dh_client_pub == NULL");
69 packet_get_bignum2(dh_client_pub);
70 packet_check_eom();
71
72 #ifdef DEBUG_KEXDH
73 fprintf(stderr, "dh_client_pub= ");
74 BN_print_fp(stderr, dh_client_pub);
75 fprintf(stderr, "\n");
76 debug("bits %d", BN_num_bits(dh_client_pub));
77 #endif
78
79 #ifdef DEBUG_KEXDH
80 DHparams_print_fp(stderr, dh);
81 fprintf(stderr, "pub= ");
82 BN_print_fp(stderr, dh->pub_key);
83 fprintf(stderr, "\n");
84 #endif
85 if (!dh_pub_is_valid(dh, dh_client_pub))
86 packet_disconnect("bad client public DH value");
87
88 klen = DH_size(dh);
89 kbuf = xmalloc(klen);
90 kout = DH_compute_key(kbuf, dh_client_pub, dh);
91 #ifdef DEBUG_KEXDH
92 dump_digest("shared secret", kbuf, kout);
93 #endif
94 if ((shared_secret = BN_new()) == NULL)
95 fatal("kexdh_server: BN_new failed");
96 BN_bin2bn(kbuf, kout, shared_secret);
97 memset(kbuf, 0, klen);
98 xfree(kbuf);
99
100 key_to_blob(server_host_key, &server_host_key_blob, &sbloblen);
101
102 /* calc H */
103 hash = kex_dh_hash(
104 kex->client_version_string,
105 kex->server_version_string,
106 buffer_ptr(&kex->peer), buffer_len(&kex->peer),
107 buffer_ptr(&kex->my), buffer_len(&kex->my),
108 server_host_key_blob, sbloblen,
109 dh_client_pub,
110 dh->pub_key,
111 shared_secret
112 );
113 BN_clear_free(dh_client_pub);
114
115 /* save session id := H */
116 /* XXX hashlen depends on KEX */
117 if (kex->session_id == NULL) {
118 kex->session_id_len = 20;
119 kex->session_id = xmalloc(kex->session_id_len);
120 memcpy(kex->session_id, hash, kex->session_id_len);
121 }
122
123 /* sign H */
124 /* XXX hashlen depends on KEX */
125 key_sign(server_host_key, &signature, &slen, hash, 20);
126
127 /* destroy_sensitive_data(); */
128
129 /* send server hostkey, DH pubkey 'f' and singed H */
130 packet_start(SSH2_MSG_KEXDH_REPLY);
131 packet_put_string(server_host_key_blob, sbloblen);
132 packet_put_bignum2(dh->pub_key); /* f */
133 packet_put_string(signature, slen);
134 packet_send();
135
136 xfree(signature);
137 xfree(server_host_key_blob);
138 /* have keys, free DH */
139 DH_free(dh);
140
141 kex_derive_keys(kex, hash, shared_secret);
142 BN_clear_free(shared_secret);
143 kex_finish(kex);
144 }